A thermal type flowmeter for measuring a flow volume of gas is provided with a flow volume detection unit for measuring a flow volume and is configured to measure the flow volume of the gas by heat transfer between the flow volume detection unit and the gas as a target of the measurement. A flow volume that is measured by the thermal type flowmeter has been widely used as an important control parameter for various devices. As a feature of the thermal type flowmeter, it is possible to measure a flow volume, for example, a mass flow volume of gas with relatively higher precision as compared with flowmeters based on other schemes.
However, it has been desired to further improve precision in measuring the flow volume of gas. For example, a vehicle with an internal combustion engine mounted thereto exceedingly requires a reduction in fuel consumption and clean emissions. In order to respond to such requirements, it is necessary to measure the volume of intake air, as a main parameter of the internal combustion engine, with high precision. A thermal type flowmeter for measuring the volume of intake air introduced into the internal combustion engine is provided with an accessory path that takes a part of the intake air and a flow volume detection unit that is arranged in the accessory path, and the flow volume detection unit measures a state of measurement target gas flowing through the accessary path by performing heat transfer with the measurement target gas and outputs an electrical signal that indicates the volume of intake air introduced into the internal combustion engine. Such a technique is disclosed in JP-A-2011-252796 (PTL 1), for example.
PTL 1 discloses a technique of a thermal type flowmeter for measuring a volume of intake air that is introduced into an internal combustion engine. The thermal type flowmeter disclosed therein is provided with an accessory path that takes a part of intake air and a flow volume detection unit that is arranged in the accessory path and is configured to measure a state of measurement target gas flowing through the accessory path by performing heat transfer with the measurement target gas and output an electrical signal that indicates the volume of the intake air that is introduced into the internal combustion engine.